What should the compression be for a 1989 60HP Johnson?

[sandman]

I am looking at a used 1989 60HP Johnson as a replacement on my pontoon boat. What should I look for when doing a compression test? Is there a way to use a meter and check voltage for all three cylinders? What else should I check before investing in a used motor?<br />Thank you for your knowledge and input!

 

[JB]

Re: What should the compression be for a 1989 60HP Johnson?

Ahoy, Sandman. All cylinders should be within 5-10# of each other and over 100#, cold.<br /><br />If the engine is where you can test it under load, do so. If not, test it in a tank or on a hose. Pull each plug wire, in turn, and see that each causes a drop in rpm and can arc at least 1/2" to the block. Be sure that it provides a strong, warm telltale stream after warm-up. Inspect the plugs after the test. They should be gray or tan, and dry.<br /><br />Gearcase oil should not be milky. If you remove the fill plug with the vent plug in, you should not get water out.<br /><br />If you buy it, be sure you "prop it out", so that over-propping doesn't shorten its life.<br /><br />I'm sure others can add to this.<br /><br />Red sky at night. . . <br />JB

 

[sandman]

Re: What should the compression be for a 1989 60HP Johnson?

Thanks JB for the good information. As a novice I need a little help. What is a "strong warm telltale stream after warm-up"? Also, what does "prop it out" and over-propping mean? The prop will need to be replaced or repaired as it has had some close encounters. I am a beginner so please understand my dumb questions are very basic.

 

[JB]

Re: What should the compression be for a 1989 60HP Johnson?

Ahoy, Sandman. The "Tell-tale" is the thin stream of water coming out of the engine that "tells" you that the water pump is pumping. If it is warm, rather than hot it tells you that the engine is not overheated.<br /><br />"Propping it out" is the selection of the correct propeller pitch for your uses of your boat. The correct prop will allow your engine to reach its best operating rpm at WOT (wide open throttle), but not exceed it. Your OMC triple should operate well at about 5500rpm. On a pontoon I would expect ideal pitch to be in the neighborhood of 11 to 15", maybe shorter if yours is a biggie. <br /><br />Over propping is use of a propeller with too long a pitch for your boat, which prevents the engine from reaching best operating speed. Its like climbing steep hills in your car in overdrive. . . very bad for the engine.<br /><br />Go to the topic; "Hey New Boater, Getting Started". Get a cup of joe first, there's a lot of good stuff there.<br /><br />Good luck and let us know how you do.<br /><br />Red sky at night. . . <br />JB

 

[sandman]

Re: What should the compression be for a 1989 60HP Johnson?

Thanks again JB. I not only went to the new boater topic. I printed and filed it for future reference. Great information by a great group! I do have a large heavy pontoon boat. I will check to see what prop is on this engine if it checks out. Any suggestions on sources for rebuild parts, cheap?